Chamber length for .300 Win Mag

[JLS]

I bought a Sinclair chamber gauge for my Christensen Arms .300 WM. Followed the directions to a “T”, did it three times, and came up with 2.670” inches consistently.

Manuals list 2.620” as max case length. Does this seem right? Based on this I’d be plenty safe trimming to 2.650”, correct? Or would you leave them a little longer?

 

[fmnjr]

umm, at the risk of looking dumb, can I ask if you have access to another 300 WM to check?

 

[Hem]

I thought you were content with the 6.5.
Sounds like you might be considering a move back to the state of opportunity.

 

[JLS]

I thought you were content with the 6.5.
Sounds like you might be considering a move back to the state of opportunity.

I bought it about a year ago.

 

[JLS]

umm, at the risk of looking dumb, can I ask if you have access to another 300 WM to check?

I don’t. Based on all of my reading, max case length should be .025” shorter than the actual chamber length to the end of the neck.

I’m sure my measurements are on. It seems like a large variance, but maybe it’s more common than I think. I’ll just trim to 2.650” and call it good.

 

[grizzly63]

I would think you would be safe but what do I know.

 

[marksjeep]

Trim to the length you think it should be, chamber an empty, resized, and trimmed piece of brass, snake a scope down the bore? Even with resized/trimmed brass you should be able to see a 0.025 gap between the case mouth and the end of the chamber.

 

[winmag]

Sounds like your chamber is almost exactly to SAAMI specifications.

300 Win Mag is supposed to be cut to 2.6440” before the taper into the throat, 2.6569” after the taper at the start of the throat.

SAAMI spec for case length is 2.620” - 0.020”, so case lengths 2.600” - 2.620” are acceptable, thereby purposefully leaving a minimum of 0.024” between the end of the case and where the chamber tapers into the throat.

The top drawing illustrates standards for loaded rounds. The bottom drawing illustrates standards for cut chambers.

 

[cahunter805]

I don’t. Based on all of my reading, max case length should be .025” shorter than the actual chamber length to the end of the neck.

I’m sure my measurements are on. It seems like a large variance, but maybe it’s more common than I think. I’ll just trim to 2.650” and call it good.

Belted mag chambers/reamers can be all over the place but your measurements seem pretty spot on. If you are getting a consistent measurement I’d trim .010-.015 shorter and run them. You will know if it’s too long and pressure will soar.

Are you setting up your sizing die to just bump the shoulder of the case?

 

[JLS]

Are you setting up your sizing die to just bump the shoulder of the case?

I’m setting the shoulder back .002”.

 

[JLS]

Sounds like your chamber is almost exactly to SAAMI specifications.

My measurements were 2.670” each time. Based on my reading on the Sinclair gauge it seats where the neck begins to taper. By my math my chamber is .025” longer